Currently for Live Tile apps you have to launch the app every 2 weeks to keep the notifications flowing.

Now in Windows Phone 8, as long as the app is Pinned, or supplying pictures or information to the lock screen, that is no longer the case, making for a much smoother running Windows Phone experience without having to manage notifications as much, and with hopefully a much more reliable live tile experience.

The video also shows that the Windows Phone team does have some passion around the lack of a notification centre, which hopefully means we can expect one in a future update.